This invention is described in New Zealand Provisional Patent Application No. 40-016, filed in March, 2002.
1. Technical Field
The present invention relates to a trim system for a watercraft with a propeller driven by an outboard motor, and more particularly to an automatically adjusting trim system for optimizing performance of a small, outboard motor-driven watercraft.
2. Background Information
Ordinarily, outboard motors are mounted on the transom of a watercraft by means of a clamping bracket that is connected to the transom. A swivel bracket is often pivotally connected to the clamping bracket, and the outboard motor is mounted on the swivel bracket. The swivel movement permits certain adjustments of the outboard motor. The outboard motor itself is supported by the swivel bracket for steering movement about a generally vertically extending steering axis.
On small, outboard motor-driven watercraft, it is a common practice to include a series of spaced-apart holes in the clamping bracket for receiving a trim pin. This trim pin position engages with the swivel bracket and can be manually adjusted before operation of the watercraft, to set the trim condition of the motor, depending on the pair of holes in which the pin is received. Other types of trim-related devices include levers or ratchets for rotating and holding the outboard in different positions, but these require manual operation and do not respond to the torque xe2x80x9cfeltxe2x80x9d by the watercraft.
Larger watercraft often have a means of adjusting the trim during operation of the watercraft, so as to accommodate the particular running conditions and improve the performance of the watercraft. Normally, trim adjustment is provided by a hydraulic trim motor that is fixed between the huff and the outboard motor, which allows the outboard motor to be moved to the desired trim position.
In order to quickly bring a watercraft up out-of-the-hole from a standstill position to an on-plane condition, it is a normal practice to trim-down the motor, lower the bow, and raise the stern of the watercraft. A disadvantage of using a hydraulic trim motor to achieve this condition is the weight, complication, and expense of the hydraulic trim system. Many smaller watercraft do not have a well-performing trim system.
Hydrofoils can also facilitate watercraft planing performance by generating lift, which forces the stern of the watercraft up and the bow down. A disadvantage of hydrofoil systems is that higher watercraft speeds or much higher motor speeds are required to generate sufficient lift with the hydrofoil to place the watercraft on-plane.
The present invention provides an automatically adjusting, yet simple, trim system for an outboard motor-driven watercraft that does not have these disadvantages, and provides the public with a useful alternative. It is a watercraft trim system for guiding rotation of a propeller mounted to the watercraft. Propeller rotation in a forward drive direction causes a thrust on the watercraft, which moves the watercraft in a forward direction. Thrust produces a torque reaction from the watercraft, which tends to raise its bow. With the trim axis placed in a planing position, the watercraft adopts a planing attitude. The trim system of the present invention stabilizes the watercraft and optimizes its performance in the water.
The present invention is an automatically adjusting trim system for a watercraft having an outboard motor mounted on its stern, including:
(a) a pivotable mounting mechanism connecting the watercraft and the outboard motor, a shaft of the motor being rotatable about a trim axis, the trim axis being horizontal and disposed perpendicular to a longitudinal axis of the watercraft, the pivotable mounting mechanism comprising a movable swing arm; and
(b) a spring mechanism comprising at least one spring, a portion of the swing arm of the pivotable mounting mechanism being pivotable against the spring;
wherein, when the motor is powered, the thrust of the motor automatically pushes the swing arm, which pushes in the spring, which changes position of the motor, lifting the stern, driving a bow of the watercraft down, and moving the watercraft into a planing position. Preferably, the spring mechanism of the trim system includes two matching compression spring each extending between a trim bracket of the pivotable mounting mechanism and a downward extending bar of the swing arm, the trim bracket being mountable to the transom of a watercraft.
Also included herein is a method for enabling an outboard motor-driven watercraft with a propeller to attain and maintain a planing attitude, including the steps of:
(a) in a first position wherein the propeller provides no thrust, pre-loading two matching, parallel, of a spring mechanism of a trim system, the springs extending between a lower portion of a swing arm and a middle bracket section of a trim bracket of the trim system, so as to bias the outboard motor in a forward direction the lower portion of the swing arm being restrained by a stop plate, the middle bracket section being removably mounted on the transom of the watercraft; and
(b) applying thrust to the outboard motor, creating a torque reaction on the watercraft, wherein the spring mechanism automatically causes the outboard motor to rotate forward about an axis of the trim system to a second position attaining a planing position.